While studying the mucosal adjuvant, cholera toxin, we recently identified It Induces Th17 cell differentiation via cAMP signaling. Canonical (I.e., induced by IL-6/TGF) and non-canonical (i.e., induced by cAMP) Th17 subsets display different cytokine homing receptors and are regulated by different combinations of transcription factors. We hypothesize that these two Th17 subsets perform different physiological tasks especially at mucosal sites. To characterize the immunoprotective vs. immunopathogenic profiles of these Th17 subsets in the G-l mucosa, we proposed 4 specific aims (SA). In SA-1 we will characterize and compare the phenotype of the in vitro generated Th17 subsets after their adoptive transfer to recipient mice. Similarly, we will assess the inflammatory vs. regulatory function of each Th17 subset in a model of colitis. To explore the physiological role of cAMP signaling in Th17 differentiation in vivo, we generated ko mice that carry a specific deletion of the stimulatory Ga protein (Gsa) in CD4 T cells (GsaCD4 ko mice). Thus, in SA-2 we will evaluate the cytokine profile of GsaCD4 ko CD4 T cells, their homing properties to lymphoid organs and G-l mucosa, and their colitogenic profile in models of intestinal inflammation. In SA-3 we will evaluate whether GsaCD4 ko CD4 T cells mediate host protection against microbial pathogens, i.e., C. rodentium and H. pylori. We will examine the function of non-canonical Th17 cells in host defense, mucosal protection and mucosal inflammation. An important translational application of these studies is the design of cAMP-based pharmacological interventions that target the regulation of CD4 T cell functions in mucosal sites. Thus, in SA- 4 we will determine whether the administration of cAMP-elevating drugs regulate mucosal defense in the animal models described above. The results from our proposed research can facilitate the future design and development of vaccines and immunotherapies aimed at the protection of different mucosal surfaces from infections and immune-mediated pathology, which are the ultimate objectives of this RFA.